Polyimide film, method of manufacture , and metal interconnect board with Polyimide film substrate

ABSTRACT

A polyimide film is produced by copolymerizing pyromellitic dianhydride in combination with phenylenediamine, methylenedianiline and 3,4′-oxydianiline in a specific molar ratio. The polyimide film, when used as a metal interconnect board substrate in flexible circuits, chip scale packages (CSP), ball grid arrays (BGA) or tape-automated bonding (TAB) tape by providing metal interconnects on the surface thereof, achieves a good balance between a high elastic modulus, a low thermal expansion coefficient, alkali etchability and film formability.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a polyimide film which has ahigh elastic modulus, a low thermal expansion coefficient, alkalietchability and excellent film-forming properties when used as a metalinterconnect board substrate on the surface of which metal interconnectsare provided to form a flexible printed circuit or tape-automatedbonding (TAB) tape. The invention relates also to a method formanufacturing such film. The invention additionally relates to a metalinterconnect board for use in flexible printed circuits or TAB tape inwhich the foregoing polyimide film serves as the substrate.

[0003] 2. Description of the Related Art

[0004] TAB tape is constructed of a heat-resistant film substrate on thesurface of which are provided very fine metal interconnects. Inaddition, the substrate has openings, or “windows,” for mountingintegrated circuit (IC) chips. Sprocket holes for precisely feeding theTAB tape are provided near both edges of the tape.

[0005] IC chips are embedded in the windows on the TAB tape and bondedto the metal interconnects on the tape surface, following which themounted chip-bearing TAB tape is bonded to a printed circuit for wiringelectronic equipment. TAB tape is used in this way to automate andsimplify the process of mounting IC chips on an electronic circuit, andalso to improve manufacturing productivity and enhance the electricalcharacteristics of electronic equipment containing mounted IC chips.

[0006] TAB tapes currently in use have either a three-layer constructioncomposed of a heat-resistant substrate film on the surface of which anelectrically conductive metal foil has been laminated with anintervening layer of polyester, acrylic, epoxy or polyimide-basedadhesive, or a two-layer construction composed of a heat-resistantsubstrate film on the surface of which a conductive metal layer has beendirectly laminated without an intervening layer of adhesive.

[0007] The substrate film in TAB tape is thus required to be heatresistant. Polyimide film in particular has been used to ensure that thesubstrate film is able to withstand high-temperature operations such assoldering when IC chips are bonded to the metal interconnects on TABtape and when the IC chip-bearing TAB tape is bonded to a printedcircuit for wiring electronic equipment.

[0008] However, the heat incurred in the process of laminating polyimidefilm with metal foil or a metal layer then chemically etching the metalfoil or metal layer to form metal interconnects may elicit differingdegrees of dimensional change in the polyimide film and metal, sometimescausing considerable deformation of the TAB tape. Such deformation cangreatly hinder or even render impossible subsequent operations in whichIC chips are mounted on the tape and the IC chip-bearing TAB tape isbonded to a printed circuit for wiring electronic equipment.Accordingly, a need has been felt for some way to make the thermalexpansion coefficient of polyimide film closer to that of the metal soas to reduce deformation of the TAB tape.

[0009] Moreover, reducing dimensional change due to tensile andcompressive forces in TAB tape on which IC chips have been mounted andwhich has been bonded to a printed circuit for wiring electronicequipment is important for achieving finer-pitch metal interconnects,reducing strain on the metal interconnects and reducing strain on themounted IC chips. To achieve this end, the polyimide film used as thesubstrate must have a higher elastic modulus.

[0010] According to the definition of a polymer alloy or blend (see“Polymer Alloys: New Prospects and Practical Applications,” in HighAdded Value of Polymer Series, edited by M. Akiyama and J. Izawa,published in Japan by CMC K.K., April 1997), block, blend,interpenetrating polymer network (IPN) and graft polymerization all fallwithin the category of processes capable of increasing the elasticmodulus of a polymer.

[0011] With respect to polyimides in particular, Mita et al. (J. Polym.Sci. Part C: Polym. Lett 26, No. 5, 215-223) suggest that, on account ofthe molecular composite effect, a blend of different polyimides can morereadily attain a high elastic modulus than a copolyimide obtained fromthe same starting materials. However, because polyimide molecules havelarge molecular cohesive forces, mere blends of such molecules tend totake on a phase-separated structure. Some form of physical bonding isneeded to inhibit such phase separation.

[0012] An interpenetrating network polymer was proposed for this verypurpose by Yui et al. (“Functional Supermolecules: Their Design of andFuture Prospects,” in New Materials Series, edited by N. Ogata, M.Terano and N. Yui, published in Japan by CMC K.K., June 1998).

[0013] A specific example of a blend according to the prior-art isdisclosed in JP-A 63-175025, which relates to polyamic acid compositions(C) made up of a polyamic acid (A) of pyromellitic acid and4,4′-diaminodiphenyl ether and a polyamic acid (B) of pyromellitic acidand phenylenediamine. JP-A 63-175025 also discloses polyimides preparedfrom such polyamic acid compositions (C).

[0014] However, the methods provided in this prior art involve firstpolymerizing the different polyamic acids, then blending them together.Because thorough physical interlocking of the type seen in aninterpenetrating network polymer cannot be achieved in this way, phaseseparation may occur during imidization of the polyamic acid. In somecases, a slightly hazy polyimide film is all that can be obtained.

[0015] JP-A 1-131241, JP-A 1-131242, U.S. Pat. No. 5,081,229 and JP-A3-46292 disclose block copolyimide films manufactured from blockcopolyamic acids composed of pyromellitic dianhydride,p-phenylenediamine, and 4,4′-diaminodiphenyl ether. This prior art alsodiscloses methods for manufacturing copolyamic acid films composed ofblock components of ultimately equimolar composition by reactingnon-equal parts of the diamines and the acid dianhydride in anintermediate step.

[0016] However, in such prior-art processes, although the polyamic acidblend solution prepared is not prone to phase separation, the molecularcomposite effect is inadequate and a satisfactory increase in rigidityis not always achieved. Moreover, because polymer production involvescopolymerization using block components in which the molecular chainsare regulated, the reaction steps are complex and reaction takes alonger time. Also, the reaction passes through a step in which thereexists an excess of reactive end groups, which tends to destabilize thepolyamic acid in the course of production, making it subject to changesin viscosity and gelation. In addition to these and other productionproblems, the above prior-art methods sometimes fail to provide a filmhaving a sufficiently high Young's modulus.

[0017] The surface of the polyimide film substrate is sometimesroughened by etching with an alkali solution prior to use so as toimprove the adhesive strength of an adhesive applied thereto. Alkalietching is also at times used to form through holes or vias forinterconnects. Accordingly, there has arisen a desire for polyimidefilms having excellent alkali etchability.

[0018] A film having good planarity is desirable for better ease ofhandling in processing operations. The planarity of the film can beimproved by increasing the stretch ratio during film production. Hence,film compositions capable of being subjected to orientation at a highstretch ratio are also desired.

[0019] Methods for producing polyimide films which satisfy suchrequirements have already been proposed. For example, JP-A 1-131241,JP-A 1-131242 and JP-A 3-46292 provide polyimide films made frompolyamic acid prepared from pyromellitic dianhydride,p-phenylenediamine, and 4,4′-diaminodiphenyl ether. The same prior artalso teaches processes for producing block component-containing polyamicacid film by reacting non-equal parts of diamine and acid dianhydride inan intermediate step.

[0020] However, the above-described prior art methods provide polyimidefilms which have properties when used as a substrate for metalinterconnect boards, which need to be improved.

[0021] It is therefore an object of the invention to provide a polyimidefilm which has a high elastic modulus, a low thermal expansioncoefficient, alkali etchability and excellent film formability when usedas a metal interconnect board substrate of a type that can be providedon the surface with metal interconnects to form a flexible printedcircuit, chip scale packages, ball grid arrays or TAB tape. Anotherobject of the invention is to provide a method of manufacturing such afilm. A further object of the invention is to provide a metalinterconnect board in which the foregoing polyimide film serves as thesubstrate.

SUMMARY OF THE INVENTION

[0022] The present invention is directed to a polyimide film made from apolyamic acid prepared from a tetracarboxylic dianhydride comprisingpyromellitic dianhydride in combination with phenylenediamine,methylenedianiline and 3,4′-oxydianiline such as to satisfy conditions(1-a) to (1-c) below:

10 mol %≦X≦60 mol %  (1-a)

20 mol %≦Y≦80 mol %  (1-b)

10 mol %≦Z≦70 mol %  (1-c);

[0023] wherein X is the mole percent of phenylenediamine, Y is the molepercent of methylenedianiline, and Z is the mole percent of3,4′-oxydianiline, each based on the total amount of diamine, andfurther wherein the tetracarboxylic dianhydride and total diamine are ina molar ratio of about 0.9 to 1.1 [0022]

[0024] In another embodiment, the present invention is directed to amethod of manufacturing a polyimide film comprising the steps of, inorder:

[0025] (A) reacting starting materials comprising (a1) a tetracarboxylicacid dianhydride comprising pyromellitic dianhydride and (a2) a firstdiamine selected from phenylenediamine, methylenedianiline and3,4′-oxydianiline, in an inert solvent to form a first polyamic acidsolution containing a block component or interpenetrating polymernetwork component of the first diamine and pyromellitic dianhydride;

[0026] (B) adding to the first polyamic acid solution prepared in step Aadditional materials comprising (b1) a tetracarboxylic acid dianhydridecomprising pyromellitic dianhydride and (b2) a second diamine and athird diamine selected from phenylenediamine, methylenedianiline and3,4′-oxydianiline, and continuing the reaction with all the materials toform a second polyamic acid solution;

[0027] (C) mixing into the second polyamic acid solution obtained instep B a chemical agent capable of converting the polyamic acid intopolyimide;

[0028] (D) casting or extruding the mixture from step C onto a smoothsurface to form a polyamic acid-polyimide gel film.

[0029] (E) heating the gel film at 200 to 500° C. to transform thepolyamic acid to polyimide wherein at least one of the first diamine,second diamine and third diamine is a phenylenediamine; at least one ofthe first diamine, second diamine and third diamine is amethylenedianiline; and at least one of the first diamine, seconddiamine and third diamine is 3,4′-oxydianiline.

[0030] In another embodiment, the invention is directed to a metalinterconnect board for flexible printed circuits or TAB tape, whichboard is produced by using any of the above-described polyimide films ofthe invention as the substrate and providing metal interconnects on thesurface thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The polyimide making up the inventive film may be a blockcopolymer, a random copolymer or an IPN polymer.

[0032] Preferred block components or IPN polymer components are polyamicacids composed of phenylenediamine and pyromellitic dianhydride, andpolyamic acids composed of 3,4′-oxydianiline and pyromelliticdianhydride. After forming a polyamic acid containing such blockcomponents or IPN polymer components, the polyamic acid is imidized togive a block component or IPN polymer component-containing polyimide.

[0033] The polyamic acid-forming reaction is divided and carried out inat least two stages. First, a block component or an IPN polymercomponent-containing polyamic acid is formed. In a second step, thispolyamic acid is reacted with additional diamine and dianhydride to formadditional polyamic acid. The polyimide polymer is formed by imidizationafter the second step.

[0034] The polyimide polymer of the present invention can be used toform a polyimide film having a good balance of properties suitable foruse as the substrate in metal interconnect boards for flexible printedcircuits, chip scale packages, ball grid arrays and TAB tapes; namely, ahigh elastic modulus, a low thermal expansion coefficient, alkalietchability, and film formability.

[0035] By additionally incorporating in the polyimide polymer a blockcomponent or an IPN polymer component, the various above properties canbe brought within even more preferable ranges. The block component orIPN polymer component used for this purpose is most preferably oneprepared by the reaction of phenylenediamine with pyromelliticdianhydride.

[0036] The diamines used in the invention are linear or rigid diaminessuch as phenylenediamine, semi-rigid diamines such as 3,4′-oxydianiline,and flexible diamines such as methylenedianiline.

[0037] The phenylenediamine used in the invention may bep-phenylenediamine, m-phenylenediamine, o-phenylenediamine, or apartially substituted phenylenediamine. The use of p-phenylenediamine isespecially preferred. In the practice of the invention,p-phenylenediamine serves to increase the elastic modulus of the film.At an amount of p-phenylenediamine less than 10 mol %, based on thetotal amount of diamine, the film obtained lacks sufficient stiffness,whereas an amount of p-phenylenediamine greater than 60 mol % results intoo low a film elongation. Preferably, the p-phenylenediamine is presentin an amount of from 20 to 50 mol %.

[0038] Methylenedianiline is produced in relatively large quantities,and so is an aromatic diamine that is inexpensive and easy to acquire.It has the effect of imparting flexibility to the film. Amethylenedianiline content below 20 mol %, based on the total amount ofdiamine, leads to an excessive increase in the unit cost of the film,whereas a methylenedianiline content greater than 80 mol % results inpoor film elongation. Preferably, the methylenedianiline is present inan amount of from 30 to 70 mol %.

[0039] In the invention, 3,4′-oxydianiline increases film elongation andimproves film formability. At less than 10 mol % of 3,4′-oxydianiline,based on the total amount of diamine, film elongation is inadequate. Onthe other hand, a 3,4′-oxydianiline content greater than 70 mole %lowers the glass transition temperature, resulting in a poor heatresistance and excessive thermal shrinkage. Preferably, the3,4′-oxydianiline is present in an amount of from 10 to 50 mol %.

[0040] The tetracarboxylic dianhydride used in the invention ispyromellitic dianhydride, although concomitant use may be made of othertetracarboxylic dianhydrides within a range in the amount of additionthat does not compromise the objects of the invention. For example, lessthan 50 mol % of biphenyltetracarboxylic dianhydride orbenzophenonetetracarboxylic dianhydride may be used.

[0041] The resulting polyamic acid is converted to the polyimide byimidization.

[0042] The elastic modulus of the polyimide film can be adjusted byvarying the proportion of phenylenediamine and 3,4′-oxydianiline in thediamine used to prepare the polyamic acid. Increasing the amount ofp-phenylenediamine improves the elastic modulus and dimensionalstability, but also has the undesirable effect of increasing moistureuptake. Increasing the methylenedianiline reduces film elongation, andmay result in poor film formability. It is thus necessary to adjust themolar ratio of the respective constituents with great care in order toachieve a good balance in the various properties.

[0043] The polyimide film of the invention can be manufactured by acombination of conventional methods for making polyimide, although apreferred method of production for easily achieving the inventivepolyimide film comprises the steps of, in order:

[0044] (A) reacting starting materials comprising (al) a tetracarboxylicacid dianhydride comprising pyromellitic dianhydride and (a2) a firstdiamine selected from phenylenediamine, methylenedianiline and3,4′-oxydianiline, in an inert solvent to form a first polyamic acidsolution containing a block component or interpenetrating polymernetwork component of the first diamine and pyromellitic dianhydride;

[0045] (B) adding to the first polyamic acid solution prepared in step Aadditional materials comprising (b1) a tetracarboxylic acid dianhydridecomprising pyromellitic dianhydride and (b2) a second diamine and athird diamine selected from phenylenediamine, methylenedianiline and3,4′-oxydianiline, and continuing the reaction with all the materials toform a second polyamic acid solution;

[0046] (C) mixing into the second polyamic acid solution obtained instep B a chemical agent capable of converting the polyamic acid intopolyimide;

[0047] (D) casting or extruding the mixture from step C onto a smoothsurface to form a polyamic acid-polyimide gel film.

[0048] (E) heating the gel film at 200 to 500° C. to transform thepolyamic acid to polyimide.

[0049] In the method of manufacturing polyimide film of the invention,conditions (1-a) to (1-c) for the polyamic acid are preferably limitedrespectively to conditions (2-a) to (2-c) below:

20 mol %≦X≦50 mol %  (2-a)

30 mol %≦Y≦70 mol %  (2-b)

10 mol %≦Z≦50 mol %  (2-c).

[0050] It is also preferable in the inventive method for thephenylenediamine to be p-phenylenediamine. The inventive method, whensubjected to the above conditions, is able to achieve even bettereffects.

[0051] The polyamic acid of the invention is generally prepared at atemperature of not more than 175° C., and preferably not more than 90°C., by reacting the above-described tetracarboxylic dianhydride anddiamine in a molar ratio of about 0.90 to 1.10, preferably 0.95 to 1.05,and most preferably 0.98 to 1.02, within an organic solvent that isnon-reactive for each of these constituents.

[0052] Each of the above constituents may be added independently andsuccessively or simultaneously to an organic solvent. Alternatively, amixture of the constituents may be added to an organic solvent. However,to carry out a uniform reaction, it is advantageous to add eachconstituent successively to the organic solvent.

[0053] If successive addition is carried out, the order in which theconstituents are added is preferably one in which precedence is given tothe diamine and tetracarboxylic dianhydride constituents used to preparethe block component or IPN polymer component. That is, the reactioninvolved in the production of a polyamic acid containing a blockcomponent or an IPN polymer component is divided into at least twostages. First, a block component or IPN polymer component-containingpolyamic acid is formed. In a second step, this polyamic acid is reactedwith additional diamine and dianhydride to form additional polyamicacid. The polyimide polymer is formed by imidization after the secondstep.

[0054] The time required to form the block component or IPN polymercomponent may be selected based on the reaction temperature and theproportion of block component or IPN polymer component within thepolyamic acid, although experience shows that a time within a range ofabout 1 minute to about 20 hours is suitable.

[0055] As discussed later in the specification, to form a blockcomponent-containing polymer, it is preferable for the diamine and thetetracarboxylic dianhydride in reaction step (A) to be substantiallynon-equimolar. To form an IPN polymer component, it is preferable forthe diamine and the tetracarboxylic dianhydride in the reaction step tobe substantially equimolar or, in cases where the reaction passesthrough a reaction step in which excess diamine is present, for the endsto be capped with a dicarboxylic anhydride. The reason for having thediamine and the tetracarboxylic dianhydride substantially equimolar or,in a reaction step involving the presence of excess diamine, for havingthe ends capped with a dicarboxylic anhydride is to make the firstpolymer component formed in these reaction steps chemically inert so asnot to be incorporated onto the ends of the polyimide polymer formed inthe subsequent reaction step. At the same time, carrying out the IPNpolymer first component-forming reaction and the subsequentpolyimide-forming reaction in the same reactor facilitates the formationof molecular composites (composites between different molecules), makihgit possible to better manifest the distinctive features of the first IPNpolymer component.

[0056] A specific example is described below of the preparation of apolyimide containing a block component or an IPN polymer componentcomposed of pyromellitic dianhydride and p-phenylenediamine by usingpyromellitic dianhydride as the tetracarboxylic dianhydride and by usingp-phenylenediamine, methylenedianiline and 3,4′-oxydianiline as thediamines.

[0057] First, p-phenylenediamine is dissolved in dimethylacetamide asthe organic solvent, then pyromellitic dianhydride is added and theblock component or IPN polymer component reaction is carried out tocompletion.

[0058] Methylenedianiline and 3,4′-oxydianiline are then dissolved inthe solution, following which pyromellitic dianhydride is added and thereaction is effected, giving a four-ingredient polyamic acid solutioncontaining a block component or IPN polymer component ofp-phenylenediamine and pyromellitic dianhydride.

[0059] It is possible in this case to control the size of the blockcomponent or IPN polymer component by adding a trace amount of3,4′-oxydianiline and/or methylendianiline to the p-phenylenediamineinitially added or by having the p-phenylenediamine and pyromelliticdianhydride initially reacted be non-equimolar and adding an amount ofend-capping agent sufficient to fully react with the excess diamine.However, to take full advantage of the effects of the block component orIPN polymer component, it is preferable to prepare an IPN polymer inwhich the p-phenylenediamine and the pyromellitic dianhydride aresubstantially equimolar.

[0060] The end-capping agent, typically a dicarboxylic anhydride or asilylating agent, is preferably added within a range of 0.001 to 2%,based on the solids content (polymer concentration). Preferred examplesof dicarboxylic anhydrides include acetic anhydride and phthalicanhydride. Preferred examples of silylating agents includenon-halogenated hexamethyldisilazane, N,O-(bistrimethylsilyl)acetamideand N,N-bis(trimethylsilyl)urea.

[0061] The end point of polyamic acid production is determined by thepolyamic acid concentration in the solution and by the solutionviscosity. Addition at the end of the process of a portion of thereactants as a solution in the organic solvent used in the reaction iseffective for precisely determining the solution viscosity at the endpoint, although adjustment is required to keep the polyamic acidconcentration from falling too low.

[0062] The polyamic acid concentration within the solution is from 5 to40 wt %, and preferably from 10 to 30 wt %.

[0063] The organic solvent is preferably selected from organic solventswhich do not react with the various reactants or the polyamic acidobtained as the polymer product, which can dissolve at least one andperhaps all of the reactants, and which dissolve the polyamic acid.

[0064] Preferred examples of the organic solvent includeN,N-dimethylacetamide, N, N-diethylacetamide, N,N-dimethylformamide,N,N-diethylformamide and N-methyl-2-pyrrolidone. Any one or mixturethereof may be used. In some cases, concomitant use may be made of apoor solvent such as benzene.

[0065] During manufacture of the inventive polyimide film, the polyamicacid solution thus prepared is pressurized with an extruder or a gearpump and delivered to the polyamic acid film producing step.

[0066] The polyamic acid solution is passed through a filter to removeany foreign matter, solids and high-viscosity impurities which may bepresent in the starting materials or which may have formed in thepolymerization step. The filtered solution is then passed through afilm-forming die or a coating head, extruded in the form of a film ontothe surface of a rotating or laterally moving support, and heated fromthe support to give a polyamic acid-polyimide gel film in which some ofthe polyamic acid has imidized. The gel film is self-supporting. Whenthe film reaches a peelable state, it is peeled from the support andintroduced into an oven, where it is heated and the solvent is removedby drying to complete imidization, thereby giving the final polyimidefilm.

[0067] The use here of a sintered metal fiber filter having a cutoff of20 μm is advantageous for excluding gel products that have formed duringthe process. A sintered metal fiber filter having a cutoff of 10 μm ispreferred, and a sintered metal fiber filter with a cutoff of 1 μm isespecially preferred.

[0068] Imidization of the interpenetrating polyamic acid may be carriedout by a thermal conversion process in which heating alone is used, orby a chemical conversion process wherein polyamic acid containing animidizing agent is heat treated or the polyamic acid is immersed in animidizing agent bath. In the practice of the invention, if the polyimidefilm is to be used in a metal interconnect circuit substrate forflexible printed circuits, chip scale packages, ball grid arrays or TABtape, chemical conversion is preferable to thermal conversion forachieving at the same time a high elastic modulus, a low thermalexpansion coefficient, alkali etchability, and film formability.

[0069] Moreover, a manufacturing process in which an imidizing agent ismixed into the polyamic acid and the solution is formed into a film thenheat-treated to effect chemical conversion offers numerous advantages,including a short imidization time, uniform imidization, easy peeling ofthe film from the support, and the ability to handle in a closed systemimidizing agents which have a strong odor and must be isolated.Accordingly, the use of this type of process is preferable to a processin which the polyamic acid film is immersed in a bath of the imidizingagent and the dehydrating agent.

[0070] A tertiary amine which promotes imidization and a dehydratingagent which absorbs the water that forms in imidization are usedtogether as the imidizing agent in the invention. Typically, thetertiary amine is added to and mixed with the polyamic acid in an amountthat is substantially equimolar to or in a slight [stoichiometric]excess relative to the amount of amic acid groups in the polymer. Thedehydrating agent is added to the polyamic acid in an amount that isabout twice equimolar or in a slight [stoichiometric] excess relative tothe amount of amic acid groups in the polymer. However, the amounts ofaddition may be suitably adjusted to achieve the desired peel point fromthe support.

[0071] The imidizing agent may be added at any time from polymerizationof the polyamic acid to when the polyamic acid solution reaches thefilm-forming die or coating head. To prevent imidization from occurringduring delivery of the solution, the imidizing agent is preferably addedto the polyamic acid solution and mixed therewith in a mixer a littlebefore the solution reaches the film-forming die or coating head.

[0072] The tertiary amine is preferably pyridine or β-picoline, althoughuse can also be made of other tertiary amines such as α-picoline,4-methylpyridine, isoquinoline or triethylamine. The amount may beadjusted according to the activity of the particular tertiary amineused.

[0073] Acetic anhydride is most commonly used as the dehydrating agent,although use can also be made of other dehydrating agents such aspropionic anhydride, butyric anhydride, benzoic acid anhydride or formicacid anhydride.

[0074] Imidization of the imidizing agent-containing polyamic acid filmproceeds on the support owing to heat received from both the support andthe space on the opposite side of the film, resulting in a partiallyimidized polyamic acid-polyimide gel film which is then peeled from thesupport.

[0075] A larger amount of heat received from the support and the spaceon the opposite side of the film accelerates imidization and allows morerapid peeling of the film. However, too much heat results in the rapidrelease of organic solvent volatiles between the support and the gelfilm, causing undesirable deformation of the film. A suitable heatquantity should therefore be selected after due consideration of boththe peel point position and potential film defects.

[0076] The gel film that has been peeled from the support is carried toan oven, where the solvent is removed by drying and imidization iscompleted.

[0077] The gel film contains a large amount of organic solvent, and thusundergoes a large reduction in volume during drying. To concentratedimensional shrinkage from such volumetric reduction in the direction offilm thickness, the gel film is generally held at both edges with tenterclips and passed through a drying apparatus, or tenter frame, by theforward movement of the tenter clips. Inside the tenter frame, the filmis heated, thereby integrally carrying out both drying (removal of thesolvent) and imidization.

[0078] Such drying and imidization are carried out at a temperature of200 to 500° C. The drying temperature and the imidization temperaturemay be the same or different, although increasing the temperature in astepwise manner is preferred. Typically, to prevent film blistering dueto removal of the solvent, a somewhat low temperature within the aboverange is used at the stage where a large amount of solvent is removed bydrying. Once the danger of film blistering has passed, the temperatureis ramped up to a higher level within the above range to accelerateimidization.

[0079] Within the tenter frame, the film can be stretched or relaxed byincreasing or decreasing the distance between the tenter clips at bothedges of the film.

[0080] Preferably, cut sheets of block component or IPN polymercomponent-containing polyimide film obtained by using chemicalconversion to effect imidization are cut from a film that has beencontinuously manufactured in the manner described above. However, asmall amount of the same type of film can be produced by a process inwhich, as described subsequently in the examples, a block component orIPN polymer component-containing polyamic acid is prepared within aplastic or glass flask, following which a chemical conversion agent ismixed into the polyamic acid solution and the resulting mixture is castonto a support such as a glass plate and heated to form a partiallyimidized self-supporting polyamic acid-polyimide gel film. The resultingfilm is peeled from the support, attached to a metal holding frame orsimilar apparatus to prevent dimensional change, and heated, therebydrying the film (removing the solvent) and effecting imidization.

[0081] Compared with polyimide films obtained by thermal conversion,polyimide films according to the invention that have been thusmanufactured by using chemical conversion to effect imidization, whenemployed as a metal interconnect circuit substrate in flexible printedcircuits, chip scale packages, ball grid arrays and TAB tape, provide ahigh elastic modulus, a low thermal expansion coefficient, a lowmoisture expansion coefficient, and a low moisture uptake. Moreover,they have excellent alkali etchability.

[0082] Therefore, metal interconnect boards for flexible printedcircuits, chip scale packages, ball grid arrays or TAB tape that aremanufactured by using the inventive polyimide film as the substrate andproviding metal interconnects on the surface thereof exhibit a highperformance characterized by an excellent balance of properties; namely,a high elastic modulus, a low thermal expansion coefficient, alkalietchability, and excellent film formability.

[0083] Preferably, the polyimide film of the invention has an elasticmodulus of at least 4 GPa, a thermal expansion coefficient of 10 to 20ppm/° C., and a moisture uptake of not more than 2%, and especially notmore than 1%. The alkali etchability is preferably such as to allowdissolution of the film. As described below, evaluation of the alkalietchability can be carried out based on the surface etch rate underalkaline conditions.

[0084] In the soldering step, the film is exposed to elevatedtemperatures close to 300° C. Hence, it is preferable for the film tohave a low thermal shrinkage. In some cases, use of the film can bedifficult if the thermal shrinkage is greater than 1%. Hence, a thermalshrinkage of not more than 1%, and especially not more than 0.1% ispreferred.

EXAMPLES

[0085] Examples are given below by way of illustration, although theexamples are not intended to limit the invention. The various filmproperties were measured as described below.

[0086] Abbreviations

[0087] DMAc dimethylacetamide

[0088] MDA methylenedianiline

[0089] 34′-ODA 3,4′-oxydianiline, also referred to as3,4′-diaminodiphenyl ether

[0090] PDA p-phenylenediamirie

[0091] PMDA pyromellitic dianhydride

[0092] Test Procedures

[0093] (1) Elastic Modulus and Elongation at Break

[0094] The elastic modulus was determined in accordance with JIS K7113from the slope of the first rise in the tension-strain curve obtained ata test rate of 300 mm/min using a Tensilon tensile tester manufacturedby Orientech Inc.

[0095] The elongation at break was obtained as the elongation when thesame test specimen broke.

[0096] (2) Thermal Expansion Coefficient

[0097] The temperature of a sample was increased at a rate of 10° C./minthen decreased at a rate of 5° C./min using a TMA-50 thermomechanicalanalyzer manufactured by Shimadzu Corporation. The dimensional change inthe sample from 50° C. to 200° C. at the time of the second rise or fallin temperature was used to determine the thermal expansion coefficient.

[0098] (3) Moisture Uptake

[0099] A film sample was held for 48 hours in a test chamber (STPH-101,manufactured by Tabai Espec Corp.) kept at 25° C. and 95% relativehumidity. The moisture uptake was the weight gain relative to the weightof the sample when dry, expressed as a percentage of the dry weight.

[0100] (4) Alkali Etchability

[0101] One surface of a polyimide film sample was placed in contact witha 1 N potassium hydroxide solution in ethanol/water (80/20 by volume) at40° C. for 120 minutes, and the film thickness before and after contactwas measured using a Litematic thickness gauge (supplied by MitutoyoCorp.). The alkali etchability was rated as shown below based on thepercent change in thickness.

[0102] Good: Change in thickness of at least 5%

[0103] Fair: Change in thickness of at least 1% but less than 5%

[0104] Poor: Change in thickness of less than 1%

[0105] (5) Warping of Metal Laminate

[0106] A polyimide-base adhesive was coated onto the polyimide film, andcopper foil was laminated thereon at a temperature of 250° C. Theadhesive was then cured by raising the temperature to a maximum of 300°C. The resulting metal laminate was cut to a sample size of 35×120 mm.The samples were held for 24 hours at 25° C. and 60% relative humidity,following which the extent of warp in each sample was measured.Measurement consisted of placing the sample on a flat sheet of glass,and measuring and averaging the height of the four corners. The extentof warping was rated as indicated below. A “Large” rating means that useof the sample as a metal interconnect board would result in handlingproblems during conveyance in subsequent operations.

[0107] Small: Less than 1 mm of warp

[0108] Moderate: At least 1 mm but less than 3 mm of warp

[0109] Large: At least 3 mm of warp

[0110] (6) Film Formability

[0111] A prepared film was biaxially oriented at the same speed in bothdirections and 400° C. on a polymeric film biaxial orientation systemfor laboratory use (BIX-703, manufactured by Iwamoto Seisakusho Co.,Ltd.), and the film surface area at break was determined. The preheatingtime was 60 seconds and the one-side stretch rate was 10 cm/min.

[0112] Excellent: Areal stretch ratio at break is greater than 1.3.

[0113] Good: Areal stretch ratio at break is 1.1 to 1.2.

[0114] Fair: Areal stretch ratio at break is 1 to 1.1. Acceptable forpractical purposes.

[0115] Poor: Areal stretch ratio at break is less than 1. Film formationis difficult.

[0116] (7) Thermal Shrinkage

[0117] The percent dimensional change before and after heating at 300°C. for 1 hour was measured in accordance with JIS-C2318.

Percent thermal shrinkage=100×(A−B)/A

[0118] where

[0119] A represents the film dimensions before heating

[0120] B represents the film dimensions after heating

[0121] Good: Less than 0.05%

[0122] Fair: At least 0.05% but less than 0.1%

[0123] Poor: More than 0.1%

Example 1

[0124] A 500 cc glass flask was charged with 150 ml ofdimethylacetamide, following which p-phenylenediamine was added to thedimethylacetamide and dissolved, then methylenedianiline,3,4′-oxydianiline and pyromellitic dianhydride were successively added.The flask contents were stirred at room temperature for about one hour,ultimately giving a solution containing 20 wt % of a polyamic acid ofthe composition shown in Table 1 in which the tetracarboxylicdianhydride and the diamines were about 100 mol % stoichiometric.

[0125] Next, 30 g of this polyamic acid solution was mixed with 12.7 mlof dimethylacetamide, 3.6 ml of acetic anhydride and 3.6 ml ofβ-picoline to form a mixed solution. The resulting solution was castonto a glass plate, then heated for about 4 minutes over a 150° C. hotplate, thereby forming a self-supporting polyamic acid-polyimide gelfilm. The film was subsequently peeled from the glass plate.

[0126] The gel film was set in a metal holding frame equipped withnumerous pins and heated for 30 minutes while raising the temperaturefrom 250° C. to 330° C., then heated for about 5 minutes at 400° C.,giving a polyimide film having a thickness of about 25 μm.

[0127] The properties of the resulting polyimide film are shown in Table1.

Examples 2 to 4

[0128] A 500 cc glass flask was charged with 150 ml ofdimethylacetamide, following which p-phenylenediamine was added to thedimethylacetamide and dissolved, then pyromellitic dianhydride was addedand the flask contents were stirred at room temperature for about onehour. Methylenedianiline and 3,4′-oxydianiline were subsequently fed tothe resulting polyamic acid solution and completely dissolved, followingwhich the flask contents were stirred at room temperature for about onehour. Next, phthalic anhydride was added in an amount of 1 mol %, basedon the diamines, and the flask contents were again stirred for about onehour, giving a solution containing 20 wt % of a polyamic acid of thecomposition shown in Table 1 in which the tetracarboxylic dianhydrideand the diamines were about 100 mol % stoichiometric.

[0129] In each example, this solution having a polyamic acidconcentration of 20 wt % was treated by the same method as in Example 1,giving polyimide films having a thickness of about 25 μm.

[0130] The properties of the resulting polyimide films are shown inTable 1. TABLE 1 Copolyimide films Thermal Elastic expansion WarpingPercent Constituents (mol %) modulus coefficient Elongation Alkali ofmetal Film thermal PMDA PDA MDA 34′-ODA (GPa) (ppm/° C.) (%) etchabilitylaminate formability shrinkage Example 1 100 40 30 30 4.2 14 70 goodsmall good good Example 2 100 40 50 10 4.1 15 50 good small good goodExample 3 100 30 50 20 3.8 20 60 good small good good Example 4 100 2070 10 3.5 19 50 good small good fair

Examples 5 to 7

[0131] A 500 cc glass flask was charged with 150 ml ofdimethylacetamide, following which p-phenylenediamine was added to thedimethylacetamide and dissolved. Pyromellitic dianhydride was then addedand the flask contents were stirred at room temperature for about onehour. Next, acetic anhydride was added in an amount of 1 mol %, based onthe diamine component, and the flask contents were again stirred forabout one hour. Methylenedianiline and 3,4′-oxydianiline were then addedto this polyamic acid solution and completely dissolved, following whichpyromellitic dianhydride was added and the flask contents were stirredat room temperature for about one hour, yielding a solution containing23 wt % of a polyamic acid of the composition shown in Table 2 in whichthe tetracarboxylic dianhydride and the diamines were about 100 mol %stoichiometric.

[0132] In each example, the polyamic acid solution was treated by thesame method as in Example 1, giving polyimide films having a thicknessof about 50 μm.

[0133] The properties of the resulting polyimide films are shown inTable 2. TABLE 2 IPN polyimide films Thermal Constituents (mol %)Elastic expansion Warping Percent First polymer (A) Second polymer (B)modulus coefficient Elongation Alkali of metal Film thermal PMDA PDAPMDA MDA 34′-ODA (GPa) (ppm/° C.) (%) etchability laminate formabilityshrinkage Example 5 40 40 60 30 30 5.2 10 80 good small good goodExample 6 40 40 60 50 10 5.1 10 70 good moderate good good Example 7 3030 70 50 20 4.6 15 70 good small good good

Comparative Example 1

[0134] A 500 cc glass flask was charged with 150 ml ofdimethylacetamide, following which methylenedianiline and3,4′-oxydianiline were added to the dimethylacetamide and dissolved,then pyromellitic dianhydride was added and dissolved. The flaskcontents were stirred at room temperature for about one hour, giving asolution containing 20 wt % of a polyamic acid of the composition shownin Table 3 in which the tetracarboxylic dianhydride and the diamine wereabout 100 mol % stoichiometric.

[0135] This polyamic acid solution was treated by the same method as inExample 1, giving a polyimide film having a thickness of about 25 μm.

[0136] The properties of the resulting polyimide film are shown in Table3.

Comparative Examples 2 to 6

[0137] Following the same general procedure as in Comparative Example 1,a 500 cc glass flask was charged with 150 ml of dimethylacetamide,following which the starting materials in the proportions shown in Table3 were successively added to the dimethylacetamide and dissolved. Theflask contents were stirred at room temperature for about one hour,giving a solution containing 20 wt % of a polyamic acid of thecomposition shown in Table 3 in which the tetracarboxylic dianhydrideand the diamine were about 100 mol % stoichiometric.

[0138] In each example, the polyamic acid solution was treated by thesame method as in Example 1, giving a polyimide film having a thicknessof about 25 μm.

[0139] The properties of the resulting polyimide films are shown inTable 3. TABLE 3 Thermal Elastic expansion Warping Percent Constituents(mol %) modulus coefficient Elongation Alkali of metal Film thermal PMDAPDA MDA 34′-ODA (GPa) (ppm/° C.) (%) etchability laminate formabilityshrinkage Comp. Ex. 1 100 0 70 30 2.5 30 50 good large good poor Comp.Ex. 2 100 50 50 0 The film ruptured during drying. Comp. Ex. 3 100 70 307 0 25 good large poor good Comp. Ex. 4 100 100 The film ruptured duringdrying. Comp. Ex. 5 100 100 2.3 32 10 good large poor poor Comp. Ex. 6100 100 4.7 18 100 good small good poor

[0140] As is apparent from the results shown in Tables 1 to 3, unlikethe two-component polyimide films prepared in the comparative examples,random copolyimide films and block copolyimide films according to thepresent invention produced from pyromellitic dianhydride,p-phenylenediamine and 3,4′-oxydianiline by a chemical conversionprocess satisfy all the desired properties (high elastic modulus, lowthermal expansion coefficient, alkali etchability, good filmformability) at once. Such characteristics make the inventive filmshighly suitable as metal interconnect circuit substrates for use inflexible printed circuits, chip scale packages, ball grid arrays and TABtape.

[0141] As demonstrated above, compared with polyimide films produced bya thermal conversion process, polyimide films according to theinvention, when used in metal interconnect circuit substrates forflexible printed circuits, chip scale packages, ball grid arrays or TABtape, exhibit a high elastic modulus, a low thermal expansioncoefficient, alkali etchability and excellent film formability.

[0142] Therefore, metal interconnect boards for use in flexible printedcircuits, chip scale packages, ball grid arrays or TAB tape which areproduced by using the polyimide film of the invention as the substrateand providing metal interconnects on the surface thereof exhibit anexcellent performance characterized by a good balance of properties:high elastic modulus, low thermal expansion coefficient, low moistureexpansion coefficient, low moisture uptake, and alkali etchability.

What is claimed is:
 1. A polyimide film made from a polyamic acidprepared from a tetracarboxylic dianhydride comprising pyromelliticdianhydride in combination with phenylenediamine, methylenedianiline and3,4′-oxydianiline such as to satisfy conditions (1-a) to (1-c) below: 10mol %≦X≦60 mol %  (1-a)20 mol %≦Y≦80 mol %  (1-b)10 mol %≦Z≦70 mol%  (1-c) wherein X is the mole percent of phenylenediamine, Y is themole percent of methylenedianiline, and Z is the mole percent of3,4′-oxydianiline, each based on the total amount of diamine, andfurther wherein the tetracarboxylic dianhydride and total diamine are ina molar ratio of about 0.9 to 1.1.
 2. The polyimide film of claim 1which is made from a polyamic acid selected from a blockcomponent-containing polyamic acid and an interpenetrating polymernetwork component-containing polyamic acid.
 3. The polyimide film ofclaim 1 or 2, wherein the phenylenediamine is p-phenylenediamine.
 4. Amethod of manufacturing a polyimide film, the method comprising thesteps of, in order: (A) reacting starting materials comprising (a1) atetracarboxylic acid dianhydride comprising pyromellitic dianhydride and(a2) a first diamine selected from phenylenediamine, methylenedianilineand 3,4′-oxydianiline, in an inert solvent to form a first polyamic acidcontaining a component selected from a block component of the firstdiamine and pyromellitic dianhydride and an interpenetrating polymernetwork component of the first diamine and pyromellitic dianhydride; (B)adding to the first polyamic acid prepared in step A additionalmaterials comprising (b1) a tetracarboxylic acid dianhydride comprisingpyromellitic dianhydride and (b2) a second diamine and a third diamineselected from phenylenediamine, methylenedianiline and3,4′-oxydianiline, and continuing the reaction with all the materials;(C) mixing into the second polyamic acid solution obtained in step B achemical agent capable of converting the polyamic acid into polyimide;(D) casting or extruding the mixture from step C onto a smooth surfaceto form a polyamic acid-polyimide gel film; and (E) heating the gel filmat 200 to 500° C. to transform the polyamic acid to polyimide; whereinat least one of the first diamine, second diamine and third diamine is aphenylenediamine; at least one of the first diamine, second diamine andthird diamine is a methylenedianiline; and at least one of the firstdiamine, second diamine and third diamine is 3,4′-oxydianiline.
 5. Themethod of claim 4, wherein conditions (1-a) to (1-c) below aresatisfied: 10 mol %≦X≦60 mol %  (1-a)20 mol %≦Y≦80 mol %  (1-b)10 mol%≦Z≦70 mol %  (1-c); wherein X is the mole percent of phenylenediamine,Y is the mole percent of methylenedianiline, and Z is the mole percentof 3,4′-oxydianiline, each based on the total amount of diamine, andfurther wherein the tetracarboxylic dianhydride and total diamine are ina molar ratio of about 0.9 to 1.1.
 6. The method of claim 5, whereinconditions (2-a) to (2-c) below are satisfied: 20 mol %≦X≦50 mol%  (2-b)30 mol %≦Y≦70 mol %  (2-c)10 mol %≦Z≦50 mol %  (2-d) wherein thetetracarboxylic dianhydride and total diamine are in a molar ratio ofabout 0.98 to 1.02.
 7. A metal interconnect board for use in flexibleprinted circuits or tape-automated bonding tape, which board is producedby using the polyimide film of claim 1 as the substrate and providingmetal interconnects on the surface thereof.